Atomic Force Microscope as a Tool for Nanometer Scale Surface Patterning
S.V. Lemeshko, S.A. Saunin and V.A. Shevyakov
Nanotechnology Instruments Europe B.V., NL
3D nanolithography, tip-induced oxidation, AFM
The progress in scanning probe microscopy (SPM) has transformed scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs) from measuring devices into technological tools. Local surface modification by scanning probe allows us to treat materials with resolution from the angstrom to micron level [1-3]. The demonstration of single electron transistor creation by LAO  opens the way to the development of industrial nanolithography processing. However, an insufficient knowledge in detailed understanding of the LAO mechanism limits the integration of this process into bulk production. The first experiments in STM tip oxidation of the hydrogen passivated Si surface was demonstrated in . It was shown that electrical and structural properties of the positive-biased surface are changed irreversibly in air at room temperature under the tip effect. The common explanation of these changes in surface topography is formation of the oxide under the tip. The tendencies obtained in various works of the oxide pattern shape and its growth kinetics on the conditions of tip-induced treatment allows us to propose an electrochemical mechanism of LAO. The significant effect of the humidity on oxidation velocity is observed in [6, 7]. This fact confirms the necessity of adsorbed electrolyte layer presence to produce oxide that is in good agreement with the electrochemical model. Moreover, there are other technological parameters that affect the oxidation kinetics. For example, the conductivity of an oxidized material affects the oxidation rate . In this work we study oxidation kinetics, and factors influencing on lateral resolution of anodic oxide grows by AFM tip-induced oxidation of ultrathin titanium films deposited on SiO2 substrate. It is shown that by adjusting process parameters the minimal oxide island diameter in 4 nm could be achieved. By using AFM special software we introduce 3D nanolithography for nanometer size image creation. In spite of the some assumptions in theoretical estimations, the model of tip-induced oxidation provided a qualitative accordance of the experimental and theoretical results. This allows us to define the key parameters of nano-oxidation with SPM. The nano-oxidation rate depends on applied voltage, oxidized material resistance and relative humidity. The oxidation rate depends on the number of electrons required for the oxide formation and the oxidation efficiency. The current efficiency also plays the important role in anodic oxidation. Thus, the silicon nano-oxidation rate is of lower order than the Ti one  because of low (lower than 10%) current efficiency . The model allows us to define optimum regimes of nanooxidation for the formation of large arrays of oxide patterns with minimum time expense.
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Nanotech 2005 Conference Program Abstract